Princess Lili B, a 3-year-old filly, broke both her front legs at the end of a timed half-mile workout Thursday morning and was euthanized later, becoming the 22nd horse killed at the track since Dec. 26.

Within hours of the incident, track owner Belinda Stronach called the deaths “beyond heartbreaking” in a statement and banned race-day substances including the popular medicine Lasix at both Santa Anita Park and Golden Gate Fields.

“We have arrived at a watershed moment,” Stronach said in a statement. “The Stronach Group has long been a strong advocate for the abolishment of race-day medication, but we will wait no longer for the industry to come together as one to institute these changes. Nor will we wait for the legislation required to undertake this paradigm shift. We are taking a stand and fully recognize just how disruptive this might be.”

Statement from Breeders' Cup regarding The Stronach Group's proposed reform initiatives announced earlier today: https://t.co/OAp5Bm9MWu
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The Stronach Group's open letter about the future of thoroughbred racing in California: https://t.co/AEMxhLXxfH

These are the first tracks in North America to ban the use of Lasix, a substance not allowed by nearly every other country, the Los Angeles Times reported.

Lasix is a diuretic given to horses hours before a race, causing them to urinate nearly 5 gallons before competing. Nineteen of the 22 horses killed had Lasix in their system, the Times reported. Records for the other three horses were not available.

The Stronach Group is also expanding bans on painkillers, anabolic steroids and shockwave therapy.